The present invention relates to processes and apparatus for making articles, and particularly to processes and apparatus for making disposable absorbent articles.
Disposable absorbent products can be fabricated in a continuous production line by the sequential addition of components to previously supplied components. This is particularly advantageous when one or more of the components can be supplied in the form of a single continuous layer. For example, in the formation of disposable absorbent articles, such as training pants, absorbent pants, diapers, incontinence articles, feminine care products, or the like, a layer is normally supplied at a point in the fabrication line in the form of a continuous roll, and absorbent pads, waist elastic bands, leg elastic bands, stretchable side panels, and/or other components can be supplied at different points in the fabrication line as discrete elements.
Various processes and apparatus are available for bringing the components of a single product together so that the components in the composite product are in a desired relation with respect to each other. In bringing these components properly together, various known processes and apparatus are used to note the position of a particular component, and then to adjust the position of subsequent components in order to properly position them.
A problem encountered with these types of processes and apparatus is that they do not adequately compensate for the stretching, or other possibly occurring defects, of a continuously moving layer. During manufacturing processes of this type, a continuously moving layer is subjected to various tensions caused by it being driven or pulled through the process for handling. This tension causes the continuously moving layer to stretch, or to relax, thereby resulting in some components being undesirably positioned or, once positioned, shifted out of position. Since it is virtually impossible to maintain a constant tension on the continuously moving layer, the degree of stretching varies throughout the process. Consequently, even though an earlier positioned component may initially be within an acceptable position range, the stretching, by way of example, of the continuously moving layer may result in the component being outside of the acceptable position range in the final composite product. Other undesirable occurrences may also result in mis-registration of a component or components.
In response to the discussed difficulties and problems encountered in the prior art, a new process and apparatus for making a disposable absorbent article, and in particular one having a registered graphic, has been discovered.
The present invention will be described herein in the context of registering and controlling the registration of a continuously moving layer and discrete components with respect to that continuously moving layer in the manufacture of disposable absorbent articles or products, such as, by way of example, a child""s training pant. Examples of other disposable absorbent articles include, but are not limited to, diapers, feminine care products, incontinence products, or the like. The terms xe2x80x9cregistered,xe2x80x9d xe2x80x9cregisteringxe2x80x9d and xe2x80x9cregistrationxe2x80x9d refer to aligning objects with respect to one another, or adjusting the alignment of objects with respect to one another to achieve proper alignment. The term xe2x80x9ccomponentxe2x80x9d can refer, but is not limited, to elastic ribbons or strips, absorbent pads, containment flaps, stretchable or non-stretchable layers, adhesive patterns, portions thereof, or the like; or a graphic. The term xe2x80x9cgraphicxe2x80x9d can refer, but is not limited, to any design, pattern, or the like.
A child""s disposable training pant can have multiple appearance-related and/or functional components registered within selected machine direction (MD) and/or cross-machine direction (CD) ranges. The term xe2x80x9cmachine directionxe2x80x9d refers to the primary direction of movement of continuously moving layers in the manufacturing process, and the term xe2x80x9ccross-machine directionxe2x80x9d refers to the direction substantially normal to the machine direction.
The present invention can provide, by way of example, a child""s disposable training pant having one or more appearance-related and/or functional components registered with other components. Examples of components that are appearance-related include, but are not limited to, the registration of graphics; highlighting or emphasizing leg and waist openings in order to make product shaping more evident or visible to the user; highlighting or emphasizing areas of the product to simulate functional components such as elastic leg bands, elastic waistbands, simulated xe2x80x9cfly openingsxe2x80x9d for boys, ruffles for girls; highlighting areas of the product to change the appearance of the size of the product; registering wetness indicators, temperature indicators, and the like in the product; registering a back label, or a front label, in the product; and registering written instructions at a desired location in the product.
Examples of functional components include, but are not limited to, absorbent pads, surge or acquisition layers, side panels, tapes, containment flaps, waist elastics, leg elastics, areas of breathability, fluid repellent areas, fluid wettable areas, adhesives or coatings, encapsulated inks, chemically-sensitive materials, environmentally-sensitive materials, heat-sensitive materials, moisture-sensitive materials, perfumes, odor control agents, inks, fasteners, fluid storage areas, textured or embossed areas, or the like.
The training pant described herein, by way of example, comprises an absorbent pad positioned between a liquid impermeable outer cover and a liquid permeable liner. The training pant further includes elastic side panels which are joined to the outer cover in order to provide elasticity thereto. The liquid impermeable outer cover can comprise two layers of material suitably joined together, in which the innermost layer can be a liquid impermeable layer and the outermost layer can be a nonwoven layer having cloth-like texture. The innermost liquid impermeable layer has a graphic printed in registration thereon. The registered graphic generally includes a visually pleasing design or pattern and is controllably registered at a designated area in the product. One registered graphic includes a graphic positioned on the front center of the product. A more detailed description of the construction and design of the above-described training pant can be found in U.S. Pat. No. 4,940,464 issued Jul. 10, 1990 to Van Gompel et al., which is incorporated herein by reference.
Described herein is a distinctive process and apparatus for registering discrete components to a continuously moving first layer. The first layer of material includes one or more reference marks provided thereon at a uniform repeat length. This uniform repeat length can be, but is not limited to, a machine product repeat length which is the length of one product during the manufacturing process. Hereinafter, the uniform repeat length is a machine product repeat length for purposes of description, but the present invention contemplates other lengths or dimensions that could serve as a uniform repeat length. The distance between two successive reference marks is determined and then used to calculate a desired speed and/or placement for adding other components to the process.
The term xe2x80x9creference markxe2x80x9d can refer, but is not limited, to a component or components or portions thereof such as elastic strips, absorbent pads, adhesive patterns, or the like; structure such as corners or edges thereof, transporting mediums such as conveyor belts or the like; visual marks, magnetic marks, electrical marks, electromagnetic marks, optical brighteners sensitive to ultraviolet radiation, or the like. All of these can be sensed, detected, or otherwise identified by an appropriate device.
The reference marks determine product length and the product per minute speed while the web speed (feet per minute) remains constant. The reference marks provide placement references which are used to generate reference signals with which the other product components can be controlled and/or registered. Since a component can serve as a reference mark, it may be identified or described as a xe2x80x9ccomponent-reference markxe2x80x9d.
The first layer can have selectively provided thereon reference marks corresponding to a respective plurality of distinct and separate locations on the layer or components. For purposes of this embodiment, the first component comprises a plurality of graphics. A first sensor generates a signal in response to each reference mark. The distance between consecutive reference mark signals is suitably measured in units of, by way of example, a driving mechanism, such as a lineshaft registration encoder. This measurement is the first component repeat length or machine product repeat length.
A second component is added to the first layer by a machine module having its own driving mechanism. The second component could be laid relative to a reference mark or the first component. A second sensor associated with this second component to be registered generates a second signal referred to as a second component signal in response to each second component that serves as a component-reference mark. The distance between consecutive second component signals is also measured in units of the same driving mechanism as the first layer, such as the lineshaft registration encoder. This measurement is the second component repeat length.
The ratio of a second component repeat length to a machine product repeat length is a gear ratio which is used to calculate a speed reference signal for speed control, so that the speed of the second component driving mechanism can be selectively controlled to adjust the speed and/or placement of a second component, such that the distance between subsequent consecutive second component signals is one machine product repeat length. This provides one second component repeat length in one machine product repeat length and is called a repeat loop. The repeat loop refers to repeatedly providing a second component at a rate substantially equal to the rate of the first layer, thereby duplicating a machine product repeat length between two successive reference marks by accurately measuring their current distance apart and calculating a desired speed reference signal for a component driving mechanism.
The second component also is controllably positioned with respect to a reference mark of the first layer. This is termed the placement loop and is performed by comparing the measured distance between a component signal and its corresponding reference mark signal to the target setpoint, and then adjusting the position of future second components to the setpoint. A xe2x80x9ctarget setpointxe2x80x9d refers to a selected value to which the placement is controlled. A xe2x80x9ccomponent signalxe2x80x9d is generated from a sensor detecting components or reference marks on the second layer. A xe2x80x9creference mark signalxe2x80x9d is generated from a sensor detecting reference marks on the first layer.
Thus, there is described herein, by way of example, a process and an apparatus for using a first layer of material, which may include one or more distinct and separate components pre-positioned thereon, and providing a simplified device for registering other components on the first layer, thereby ultimately providing individual disposable absorbent articles. One process of the present invention uses consistently placed or positioned reference marks on the continuous first layer to generate reference signals throughout the entire manufacturing process.
One advantage of the process and apparatus is that it provides a unique machine product repeat length change capability during the manufacturing process by providing the ability to automatically change the speed and/or feed rate of various modules that provide selected components. Thus, the speed, registration, and other desired changes needed for a machine product repeat length change for, by way of example, manufacturing different sizes or types of products, can be accomplished by changing the first layer with another layer having a different length between reference marks, in which the different length corresponds to the change in product size or type. The present invention automatically senses these changes and controllably adjusts the repeat loop and the placement loop for other components.
The first layer of material can be, for example, a continuous polyethylene film preprinted with one or more reference marks per product. The use of the term xe2x80x9clayerxe2x80x9d can refer, but is not limited, to any type of substrate, such as a woven web, nonwoven web, films, laminates, panels, composites, elastomeric materials, or the like. A layer can be liquid and air permeable, permeable to air and impermeable to liquids, impermeable both to air and liquid, or the like. The reference marks are preprinted or otherwise arranged such that they will be positioned at the same designated area in each finished product. The term xe2x80x9cfinishedxe2x80x9d or xe2x80x9cfinalxe2x80x9d, when used with reference to a product, means that the product has been suitably manufactured for its intended purpose.
The process of the present invention senses the first layer""s reference marks that are moving at a desired constant rate of speed and generates a reference signal for other machine components and modules. In particular, there is provided accurate, real time information during the production process, and rapid adjustments to the process to provide the desired registration of subsequent components in the final products. Additionally, process control variables can be automatically modified in response to changes in machine product repeat length in accordance with preprogrammed instructions.
Earlier, a reference mark was described with some examples. In the embodiments described hereinafter, the reference mark selected is an optical brightener which can be configured in any desired size or shape. The reference mark may comprise, for instance, a generally rectangular region having a machine direction dimension of about 19 millimeters and a cross-machine direction dimension of about 37 millimeters. Optionally, other dimensions may be employed. It is to be understood that the various detecting and sensing devices described herein are to be appropriately compatible with the type of associated reference mark that is to be detected or sensed. The term xe2x80x9cassociatedxe2x80x9d refers to the reference mark either being directly on a component that it represents, such as a graphic, or being selectively spaced therefrom. The optical brightener is provided to be sensitive to ultraviolet radiation. The optical brightener is, for example, capable of absorbing ultraviolet radiation and then fluorescing to emit light spectra that can be sensed by an appropriate and compatible detector or sensor. Ultraviolet radiation is generally understood to include electromagnetic radiation having wave lengths ranging from about 20-400 nanometers. Suitable optical brighteners include, for example, UVITEX OB manufactured by Ciba-Geigy, and LEUCOPURE EGM manufactured by Sandoz Chemicals Corporation.
Where the reference mark comprises ultraviolet sensitive optical brighteners, a suitable detector or sensor is a UV activated detector, such as a SICK detector model LUT 3-6 available from SICK OPTIK ELEKTRONIK, Inc., a business having offices in St. Paul, Minn.
Other suitable reference marks, as well as sensors, computer devices, motors, and the like are described in U.S. Pat. No. 5,235,515 issued Aug. 10, 1993 to Ungpiyakul et al.; U.S. Pat. No. 5,359,525 issued Oct. 25, 1994 to Weyenberg; and U.S. Pat. No. 4,837,715 issued Jun. 6, 1989 to Ungpiyakul et al.; the contents of each of which are incorporated herein by reference.
The described process and apparatus utilize several devices, and representative devices include encoders, signal counters, and sensors or detectors. An encoder generates a pulse train, which is a selected number of pulses per revolution of the encoder shaft, for subsequent counting and control. A signal counter receives a generated pulse train from an encoder, and counts the pulses for subsequent query. A sensor or detector senses an occurrence or interruption in a process and generates a signal in response thereto.